Abstract
Fertilization has been shown to affect interactions between root hemiparasitic plants and their host plants, alleviating damage to the hosts by parasitism. However, as a majority of studies were conducted in pot cultivation, the influence of fertilizer application on root hemiparasites and the surrounding plant community in field conditions as well as relevant mechanisms remain unclear. We manipulated soil nutrient resources in a semi-arid subalpine grassland in the Tianshan Mountains, northwestern China, to explore the links between fertilization and plant community composition, productivity, survival, and growth of a weedy root hemiparasite (Pedicularis kansuensis). Nitrogen (at a low rate, LN, 30 kg N ha-1 year-1 as urea; or at a high rate, HN, 90 kg N ha-1 year-1 as urea) and phosphorus [100 kg ha-1 year-1 as Ca(H2PO4)2⋅H2O] were added during two growing seasons. Patterns of foliar nutrient balances were described with isometric log ratios for the different plant functional groups receiving these fertilization regimes. Fertilization with LN, HN, and P reduced above-ground biomass of P. kansuensis, with above-ground biomass in the fertilization treatments, respectively, 12, 1, and 39% of the value found in the unfertilized control. Up to three times more above-ground biomass was produced in graminoids receiving fertilizers, whereas forb above-ground biomass was virtually unchanged by the fertilization regimes and forb species richness was reduced by 52% in the HN treatment. Fertilization altered foliar nutrient balances, and distinct patterns emerged for each plant functional group. Foliar [C | P,N] balance in the plant community was negatively correlated with above-ground biomass (P = 0.03). The inhibited competitiveness of P. kansuensis, which showed a much higher [C | P,N] balance, could be attributed to reduced C assimilation rather than mineral nutrient acquisition, as shown by significant increase in foliar N and P concentrations but little increase in C concentration following fertilization.
Highlights
Root hemiparasitic plants are green plants with retained photosynthetic capability, but still partially depend on a host plant for water, mineral nutrients and in many cases carbohydrate supply (Press, 1995; Irving and Cameron, 2009; Tešitel et al, 2011)
Plant species richness and canopy cover of different plant functional groups were comparable among blocks (Figure 2)
Plant species richness was not affected by fertilizer treatment during the first growing season, but significantly reduced by 51% in HN treatment (P < 0.05) during the second growing season compared to the unfertilized control (Figure 2A)
Summary
Root hemiparasitic plants are green plants with retained photosynthetic capability, but still partially depend on a host plant for water, mineral nutrients and in many cases carbohydrate supply (Press, 1995; Irving and Cameron, 2009; Tešitel et al, 2011). Root hemiparasitic plants can alter plant community structure and plant diversity by changing competitive relationships between host and non-host plant species (Hedberg et al, 2005; Borowicz and Armstrong, 2012; Bao et al, 2015), causing significant effects on above and below-ground ecosystems at various trophic levels (Bardgett et al, 2006; Hartley et al, 2015) Despite their ubiquity in territorial ecosystems (Press, 1995) and being long considered as keystone species (Press and Phoenix, 2005), investigations of root hemiparasitic plants under field conditions are limited when compared with numerous studies of other plant species. How other root hemiparasites interact with the surrounding plant community under various environmental conditions remains unexplored
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